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May 14, 2012-- For many people, preparing for a colonoscopy is sometimes more daunting than the procedure itself.

You typically stop eating solid food for at least a day, and then drink what seems like gallons of liquid to clean out your bowel. You need to stay close to a bathroom, because you will be going and going and going.

Dread of the prep might be one reason why, according to government estimates, about 4 out of 10 Americans ages 50-75 don't meet recommendations for colorectal cancer screening. One common screening option is a colonoscopy every 10 years for those at average risk for colorectal cancer.

But what if you didn't have to purge your colon? Might that increase screening rates?

Michael Zalis, MD, an associate professor of radiology at Harvard, thinks so. Zalis led a new study that suggests a laxative-free "virtual colonoscopy" -- which uses computerized tomography, or CT scanning, to create a three-dimensional view of the colon's interior -- can pick up about 90% of precancerous polyps that are 10 millimeters (0.4 inches) or larger.

That's much better than not detecting any at all because of skipped screenings, says Zalis, director of CT colonography (a medical term for virtual colonoscopy) at Massachusetts General Hospital.

"Colon cancer is a common disease, and it's almost completely preventable," he says. "If we could come up with a more patient-friendly form of screening, we might very well get more people to participate." Colon cancer kills more Americans than any other type of cancer except lung cancer.

Zalis' team studied people 50 to 85 years old who were already scheduled for a conventional colonoscopy. None were at high risk of colon cancer.

The patients first underwent a laxative-free virtual colonoscopy and then a traditional colonoscopy, so the researchers could compare the two methods.

Electronic 'Cleansing'

Before the virtual colonoscopy, the patients were asked to stick to a low-fiber diet and consume tiny amounts -- "about what you might have in a ketchup packet," Zalis says -- of a contrast agent to label fecal material in the colon. Software programs developed by Zalis and his collaborators electronically "cleansed" the feces from the virtual colonoscopy images.

The researchers found that the laxative-free CT colonography accurately identified 9 out of 10 patients with precancerous polyps 10 millimeters or larger. Generally, about 15% of virtual colonoscopies detect an abnormal growth that must be removed through a conventional colonoscopy, Zalis says.

"Accepted practice" in colon cancer screening is that precancerous polyps that are 6 millimeters or larger should be removed, the scientists write. However, they add, about 91% of the most dangerous polyps are at least 10 millimeters in size.

People in Zalis' study said they preferred the comfort and preparation for the virtual colonoscopy over that for the conventional colonoscopy.

A Dutch study published in January had similar results. Researchers randomly divided people ages 50-75 into two groups: One was invited to have a conventional colonoscopy, the other a laxative-free virtual colonoscopy. While colonoscopy picked up more advanced abnormal growths, a higher percentage of people invited to have CT colonography agreed to be screened.

Virtual Colonoscopy Uncommon

Although virtual colonoscopy eliminates another off-putting aspect of conventional colonoscopy -- the need to insert a long, thin tube called a colonoscope through the entire length of the colon -- relatively few Americans have opted for the procedure.

In 2010, only about 1 in 100 Americans aged 50-75 reported ever having a virtual colonoscopy, according to CDC and National Cancer Institute data published this month.

In 2008, the American Cancer Society endorsed CT colonography every five years as an acceptable colon screening method. But Medicare doesn't routinely cover the procedure, Zalis says. "Appropriately, there's a high bar placed on screening."

Private insurers tend to follow Medicare's lead, so virtual colonoscopy is not widely reimbursed. As a result, Zalis says, relatively few doctors have learned how to do it.

Zalis says Massachusetts General is not yet promoting laxative-free CT colonography because his findings need to be confirmed by other researchers. However, he says, if a patient who's never been screened asks about having a laxative-free colonography, "we'd definitely do the exam."

The findings of Zalis' study are "intriguing," says gastroenterologist Samir Gupta, MD, an assistant professor of internal medicine at the University of Texas Southwestern Medical Center in Dallas.

"The game-changer for CT colonography would be if they could do minimal prep, laxative-free exams and have high sensitivity for most polyps and cancers," Gupta says. "I think this study is a very good proof-of-concept study. But it's not ready for prime time."

Zalis' study appears in the current issue of the Annals of Internal Medicine.